1. Field of the Invention
The present invention relates to electrical appliances, and more specifically to an LED replacement for low voltage lamps that can function as a replacement for a low voltage lamp, such as an MR16 halogen lamp.
2. Description of the Related Art
“MR” stands for multifaceted reflector, a pressed glass reflector with the inside (reflecting side) surface composed of facets and covered by a reflective coating. The facets provide optical control by gathering the light from the filament to create a concentrated beam of light. The reflectors of some MR lamps have a smooth inside surface instead of facets however they are typically still called MR lamps. The typical MR lamp has a single-ended quartz halogen filament capsular light source that is typically powered by a transformerless, electronic power supply. The electronic power supply should be designed to accommodate typical MR-16 lamp power ratings, which may range from 10 to 100 watts, depending on the lighting application. MR-16 lamps are generally operated using voltages lower than 120 volts, nominally 12 volts. However, it is not uncommon to find an MR-16 lamp having an operational voltage of 6 or 24 volts. A switching power supply is needed to reduce the line voltage from 120 or 240 volts to the appropriate level for these lamps. Most MR-16 low-voltage lamps are equipped with a base having two electrical contact pins. However, other bases, such as the bayonet style or turn and lock style, may be utilized.
Typically low voltage lighting utilizes a step down magnetic transformer that operates on 120 volts AC and produces an output of approximately 12 volts AC at approximately 60 Hz. This frequency allows the LEDs to operate without causing a visible flicker in their output. However, in the event that a transformerless switching power supply is used, problems arise, in that an electronic transformer generally has an oscillator that requires a load in the output before it will switch on and produce current to the output. This load varies with the design of the electronic transformer, but is typically set at 8-10 watts. If the transformer does not sense the load to be at this level, the transformer will fail to start. Typically, LED-based replacement light sources present a load to the transformer that is ten percent of the transformer rating, which is below the transformer “ON” set point. Moreover, the output frequency that the switching power supply oscillator is set to may be many times higher than the standard 60 Hz line frequency that a magnetic transformer provides. The frequency is high enough that it produces harmonics in the drive circuitry of the LED light source. Since LEDs have an 8-10 nanosecond rise time, these harmonics are of sufficient amplitude to effectively turn the LEDs on and off at a frequency that is a subharmonic of the oscillator frequency, thereby causing the LED source to flicker at a rate that becomes obvious to a person viewing the light.
Attempts have been made to replace the halogen light source of MR-16 and other low voltage lamps with an LED (light emitting diode) light source. The aforementioned common problem encountered when an LED light source is utilized is that the LED's do not draw enough current to activate the switching power supply. Also switching power supplies may from time to time output transient spikes of voltage that may damage the delicate LED sources in an LED replacement lamp.
Thus, an LED replacement for low voltage lamps solving the aforementioned problems is desired.